Moiré Quasibound States in the Continuum

Area of Science:

• Photonics and Materials Science
• Explores novel optical phenomena in engineered materials.

Background:

• Moiré structures, like twisted bilayer graphene, exhibit unique flat bands.
• Bound states in the continuum (BICs) offer potential for superior optical device design.
• Combining these concepts can lead to new exotic optical states.

Purpose of the Study:

• To introduce and demonstrate a new optical state, the moiré quasi-BIC, in twisted bilayer photonic crystal slabs.
• To investigate the dual characteristics of moiré flat bands and quasi-BICs in this new state.
• To showcase the enhanced performance of moiré quasi-BICs for applications like second-harmonic generation.

Main Methods:

• Development of an effective model at the center of the Brillouin zone to explain moiré flat band formation.
• Numerical demonstration of moiré quasi-BIC formation by tuning interlayer coupling and twist angle.
• Simulation of enhanced second-harmonic generation (SHG) using a wide-angle optical source.

Main Results:

• Successfully constructed and numerically demonstrated the moiré quasi-BIC in twisted bilayer photonic crystals.
• Showcased that moiré flat bands are formed by balancing interlayer coupling and twist angle.
• Observed that decreasing the twist angle leads to a perfect BIC with suppressed radiation loss.
• Demonstrated significantly improved SHG efficiency using moiré quasi-BICs compared to dispersive quasi-BICs.

Conclusions:

• Moiré quasi-BICs represent a novel optical state with combined moiré flat band and quasi-BIC properties.
• This new state offers a pathway to enhanced optical functionalities, particularly in nonlinear optics.
• The findings pave the way for designing advanced optical devices with improved performance.